The Nuclear Safety and Security Commission on Wednesday said the chief of the Gori-1 nuclear power plant had decided not to report a power outage at the unit on Feb. 9 to higher authorities.

The panel last week launched a probe into the temporary power failure at the Gori-1 unit in Busan and why it was only reported to the head of the Korea Hydro and Nuclear Power Co. more than a month later.

“The chief of the Gori-1 unit entered the main control room during the power loss and decided not to report the accident to the KHNP and the NSSC in a meeting with senior staff after the power came back on,” the NSSC said in a press release.

“According to related rules, the NSSC plans to press charges against those responsible for the delayed reports and omitting of records to cover up the accident.”

The commission said the Gori-1 unit staff deliberately left out records about the accident in the daily operation log to cover it up, and reported the power loss to the KHNP on March 8 upon inquiries from outside.

The KHNP top management including the chief executive learned about the accident on March 10, the NSSC said.

External power supply to the Gori-1 unit was suspended on Feb. 9 because a worker did not follow the orders of his supervisor as he tested the protection system for the power generator.

The emergency diesel power generator, which is supposed to automatically supply power to the reactor, did not work due to a defect in the air supply valve, according to the NSSC.

During the power loss that lasted for 12 minutes, the temperatures of the cooling water in the reactor went up from 36.9 to 58.3 degrees Celsius and the spent fuel storage tank from 21 to 21.5 degrees Celsius, but it did not affect the safety of nuclear fuel or cause radioactive leaks.

To prevent similar cases in the future, the NSSC said safety regulators will watch all information and reports related to nuclear safety from the power plants around the clock and establish a system to automatically receive immediate reports.

All nuclear power stations will come under special inspections with members of the NSSC and the Korea Institute of Nuclear Safety present by the end of April.

The air supply valve of the emergency diesel power generator at Gori-1 unit will be replaced with a new one and moveable diesel power generators will be placed.

The number of checkup points during regular safety inspections will be increased from 57 to 100, and the number of safety regulation staff will be gradually raised from the current 20 (five per nuclear plant site) to 100 (25 per site), the NSSC said.

By Kim So-hyun (sophie@heraldcorp.com)